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Concept paper annotated outline
EC-68/Doc. 4.5 (1)
Executive Summary
th
In June 2015, the 17 World Meteorological Congress requested a plan for an Integrated Global
Greenhouse Gas (GHG) Information System (IG3IS). In December 2015, the UNFCCC nations
forged the Paris Agreement, codifying the idea of nationally determined contributions (NDCs).
These nationally appropriate pledges to reduce GHG emissions serve to unify all nations in an
effort to slow and then stop global climate disruption. These pledges vary by nation, geographical region, and economic ability. Regardless of the strategies and mechanisms applied, the
ability to implement long-term policies and manage them effectively will require consistent, reliable, and timely GHG emissions information. There is need for a framework capable of
accepting and promoting a range of advanced GHG emission quantification capabilities that will
improve the quality of and confidence in GHG emission inventories. The IG3IS will be such an
information source and framework that will join atmospheric GHG composition and flux measurements and other observations (the “top-down”) with spatially and temporally explicit
socioeconomic emission inventory data (the “bottom-up") to better inform policies and measures.
“Better” means the timely delivery of quantitative information at scales relevant to the decisions
being made.
A planning team was established to compile information and develop a plan to motivate action. It
has developed the following vision and mission for IG3IS.
Vision: Nations, sub-national governments, businesses and individuals are able to make
evidence-based decisions that reduce climate-disrupting greenhouse gas emissions while
increasing wellbeing and equity in society.
Mission: Support the success of post-COP21 actions of nations, sub-national governments, and the private sector to reduce climate-disrupting GHG emissions through a
sound scientific, measurement-based approach that reduces the uncertainty of national
emission inventory reporting, locates, quantifies, and prioritizes previously unknown
emission reduction opportunities, and provides nations with timely and quantified guidance on progress towards their emission reduction strategies and pledges (e.g., NDCs).
This Concept Paper describes a strategic progression of confidence-building steps of near-, mid-,
and long-term objectives and will be used to guide the next step of IG3IS implementation planning. Near and mid-term objectives are focused on applying demonstrated capabilities to meet
present, yet unmet, information requirements of decision-makers to quantify GHG emissions and
their changes over time. These objectives will be accomplished with existing and new measurements and modelling tools inside a framework of measurement standards and modelling metrics.
Analogous to the development of numerical weather prediction and its architecture of observations and models, IG3IS has a long-term vision for a GHG analyses and forecast system that will
incorporate multiple coordinated satellites, aircraft, balloons, and ground observations in a system
of systems. The first step of implementation planning will be to collect detailed user requirements, which will guide the formulation of the needed measurement, modelling, and data delivery
infrastructure.
This Concept Paper provides background details for Executive Council document EC68/Doc. 4.5(1) and requests Executive Council endorsement and support to proceed to the next
steps of IG3IS implementation planning, as well as support for execution of that plan from the
Members and the Secretary-General.
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1. Motivation for an IG3IS
Accurate and precise atmospheric measurements of greenhouse gas concentrations have revealed
the rapid and unceasing rise of global GHG concentrations due to human socioeconomic activity.
Accurate and precise long-term observations also show a resulting rise in global temperatures and
evidence of negative impacts on society. In response to this mounting evidence, nations, subnational governments, private enterprises and individuals are establishing and accelerating efforts
to reduce GHG emissions while meeting the needs for global development and increasing energy
use.
Now, with appropriate investments, the same evidence-based scientific approach that rang the
climate change alarm bell stands ready to guide us along solution pathways and provide metrics
for the success of the solutions. With this motivation, WMO and its partners have called for an
Integrated Global GHG Information System1 (IG3IS). The IG3IS will serve as an international
coordinating mechanism to establish and propagate consistent methods and standards to help
ensure the success of additional and valuable emission-reduction actions. For the IG3IS initiative
to succeed the end-users must understand, trust, and recognize the value of the information they
will receive, and act more effectively in response. Over time, the IG3IS framework will be capable of promoting and accepting advancing technical capabilities (e.g., new satellite observations)
continually improving the quality of and confidence in such information.
Leading up to COP15 in Copenhagen December 2009, the research community conducted a
number of studies [e.g., Verifying Greenhouse Gas Emissions: Methods to Support International
Climate Agreements (NAS 2010); GEO Carbon Strategy (GEO 2010); IPCC Task Force on National GHG Inventories: Expert Meeting Report on Uncertainty and Validation of Emission
Inventories (IPCC 2010)] that reported on the state of carbon cycle and GHG research, and on the
readiness of atmospheric GHG concentration measurements, combined with other forms of data
and model analyses to independently evaluate and improve the accuracy of the traditional ”bottom-up” GHG emission inventories. In 2010, these studies concluded that with key research
investments, increased density of well-calibrated atmospheric GHG measurements, and improvements in atmospheric transport modelling and data assimilation capabilities, a GHG
information service framework could be achieved that would serve the evolving needs of policies
and actions to reduce GHG emissions.
Out of COP15 came a recognition that an approach based on a single metric and binding commitments was not a politically feasible approach to a post-Kyoto agreement on greenhouse
reductions. Rather, an approach that embraces the unique needs and conditions of the memberstates should drive definition of their pledges and goals. This was the rationale behind the Nationally Determined Contribution (NDC) approach approved at the COP20 in Lima and that enabled
success at the COP21 in Paris.
The IG3IS Planning Team is applying these lessons learned from the UNFCCC negotiation success. Unlike the aforementioned reports published in 2010, the IG3IS plan will not be solely
focused on the long-term vision for a comprehensive, totally independent integrated GHG information system. Instead, the IG3IS plan begins with practical and focused near-term objectives.
The IG3IS resolution approved by the 17th World Meteorological Congress in June 2015 refers to an “Integrated Global Greenhouse Gas Information System.” The IG3IS Planning Team suggests substituting the
word “Services” in place of the word “System” as a better representation of the IG3IS initiative’s mission.
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The IG3IS Planning team defined a set of questions that must be answered with criteria for selecting these confidence-building, near-term objectives:

What GHG emissions information do decision-makers require to increase the quality
of their decisions?
 Are there research capabilities with demonstrated skill to meet these information
needs in a quantitative and timely way?
 What valuable and additional outcomes will result?
 Will stakeholders see this value and be early and active partners in this effort?
The IG3IS objectives are described in section 4. For the near-term objectives, both the policy applications and the technical skill are at hand and are well matched. The mid-term goals represent
the opportunities for which the policy application requirements and the technical readiness to
meet the information needs are both incipient. For example, the Paris Agreement sets a 2°C limit
on global warming, while recognizing that the current sum total of the emission reduction pledges
from current NDCs falls short of achieving this goal. A foundation of the agreement is “global
stocktaking” now and in the future with the intent of tracking the progress of NDCs every 5 years.
Inventories built according to the IPCC Task Force on National GHG Inventories (TFI) 2006
Guidelines will have a long latency (in 2023 the inventories will be based on data from 2021 or
earlier) and may be inadequate for desired stocktaking. However, a combined approach based on
the IPCC TFI protocols and the IG3IS methods (atmospheric measurements, remotely sensed and
in situ activity data, and modelling systems) will be able to deliver timely, year-to-year, situational awareness of national emissions for effective “global stocktaking” and better management of
NDCs.
2. Goals of IG3IS
Partnerships, such as the proposed IG3IS partnership with UNEP, must be established that will
help WMO to go beyond merely engaging in conversations with the “decision-making” communities. To have the best chance of meeting our ultimate IG3IS success-criteria, we need the
decision-makers to be part of the planning process. We need to transition from stakeholder engagement to stakeholder entrainment, where they participate in specifying the requirements for
the near- and mid-term IG3IS objectives, and they are exposed to state-of-the-art techniques
emerging from the scientific community that may open new opportunities and information needs.
A present and on going example is the collaboration between the United Kingdom Department of
Energy and Climate Change (DECC) and the UK Met Office. The DECC is responsible for reporting national emission inventories to the UNFCCC and the UK Met Office provides DECC
with atmospheric model analyses of atmospheric concentration measurements to guide improvements to the DECC reported inventories. By combining accurate atmospheric measurements with
enhanced socioeconomic activity data and model analyses we can meet the overarching goals of
IG3IS to:

reduce uncertainty of emission inventory reporting,

locate, quantify and prioritize previously unknown emission reduction opportunities, and

provide national and sub-national governments with timely and quantified guidance on progress towards their emission reduction strategies and pledges (e.g.,
NDCs for nation-states).
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An effective IG3IS will provide on-going, observation-based information on the relative success
of GHG management efforts on policy-relevant scales and the response of the global carbon cycle
to a warming world.
3. IG3IS Principles
Implementation of an IG3IS requires that all elements of the system provide accurate, consistent
and timely information useful for a broad range of policy uses, accommodate future policy
changes, and take advantage of advances in emission inventory methods and information.
These are the principles by which IG3IS will achieve its objectives:







IG3IS will serve as an international coordinating mechanism and establish and propagate consistent methods and standards,
The IG3IS credibility rests upon the undisputed and high-quality atmospheric concentration measurement standards disseminated by the WMO GAW with very active
participation by the international metrology community.
IG3IS will provide a common framework for development of the good practices utilizing diverse measurement and analysis approaches inside a framework of standards.
Stakeholders are entrained in planning and implementation from the beginning to ensure that information products meet user priorities and deliver the foreseen value.
The system must be practical and focused on where the scientific and technical skill
is proven, the use-case exists and the decision-maker recognizes value.
Success-criteria are that the information provided guides additional and valuable
emission-reduction actions.
IG3IS must mature in concert with the evolution of user-needs, policy and technical
skill.
4. Near- and Mid-term Objectives
The near- and mid-term objectives are designed to demonstrate early success. Current efforts
have already partially demonstrated this in some areas (e.g., national emission inventories improvements, methane leakage from the oil and gas sector, urban emissions). The initial focus of
the work is development of high-level recommendations to establish the scope of the system in a
systematic stepwise manner. These objectives will address the need to reduce greenhouse gas
emissions around the globe, while IG3IS evolves with increasing technical skill, scientific
knowledge, and policy demands.
Table 1. Near-, mid-, and long-term IG3IS objectives in support of greenhouse gas emission
reduction efforts
Near-term (1-3 years)
Mid-term (3-10 years)
Long-term (>10 years)
Provide guidance for nations
applying atmospheric measurement and inverse methods
for enhanced national inventory reporting (e.g., UK and
Swiss examples)
Provide high-frequency, timely trend information for
“global stocktaking”; radiocarbon and other tracer
measurements to distinguish
biogenic from fossil fuel CO2
emissions
Multi-gas atmospheric inversion analyses for sector
specific attribution of emissions
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Generate user interface and
propagate existing urban GHG
estimation information to
global cities; pioneer new
techniques using HR remote
sensing activity data. Initial
sensor deployment
Demonstrate capacity sharing
with local urban partners at a
constellation of flagship cities.
Operationalize prognostic
capability within urban planning. Mature sensor
deployment
Integration across scales, multi-species; global scale
independent integration
Propagate to other global facilities the methods and
standards developed in the
USA for detection and attribution of CH4 emissions from
the oil & gas supply chain
Apply these methods and
standards to methane emissions from the agricultural
sector
Ability to provide complete
attribution to sectors
The IG3IS will benefit from the continued evolution of research successes and will depend on a
tiered observing system architecture employing surface-based, airborne, and satellite-borne sensors appropriate for the given application and analyses. The ability of IG3IS to meet a number of
its objectives will require investment in the latest techniques for building temporally and spatially
disaggregated inventories from advanced data mining from non-traditional sources of socioeconomic activity. These will be used as prior information for some analyses and applications, but at
other times IG3IS will rely solely on atmospheric measurements to independently evaluate these
bottom-up inventories.
A brief description of each objective is provided here.
4.1 Atmospheric Concentration Measurements and Analyses Assisting National-Scale Greenhouse Gas Inventory Reporting
Through the UNFCCC reporting process, the naExample from UK report to UNFCCC: HFC-134a
tional governments of Annex 1 countries have the
• Significant mismatch throughout the entire timeseries of emissions, inversion is ~50% lower than
responsibility to annually report their greenhouse
inventory.
gas emissions by sector and gas. These data are
• Inverse modeling for top-down estimates done by
UK Met Office.
collected following strict guidelines developed
• Investigated the refrigeration model used by
inventory compilers, key variables to be reand maintained by the IPCC Task Force on Naconsidered by DECC:
• Refill rate
tional GHG Inventories (IPCC TFI) by combining
• Uptake rate
source-specific emission factors with activity data,
a process often called “bottom-up”. Atmospheric
inverse modelling can support this process by
providing an independent “top-down” quantification of emissions. The United Kingdom and
Fig. 1: UK country showing the value of top
Switzerland already successfully include “topdown inversions for reporting of HFC-134a to
down” analyses to guide improvements to their
the UNFCCC.
reporting. An IG3IS near-term objective is to
propagate good practices and establish quality metrics for these top-down methods. The IG3IS
initiative has already made progress on this objective through participation in a recent IPCC TFI
Expert Meeting. This near-term IG3IS objective was presented to the IPCC TFI members who
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Emissions (kt)
6
5
4
3
Mace Head - error bars
represent the 5th and
95th percentiles
2
DECC - error bars
represent the 2.5th and
97.5th percentiles
1
UK GHGI
-
Global Climate Observa8on: the Road to the Future
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4 March 2016
decided to include the IG3IS approach in the new round of IPCC TFI assessment to update and
revise their 2006 Inventory Guidelines.
4.2
GHG emissions estimation in Large Urban Source Regions
Cities and their power plants are the largest sources of greenhouse gas emissions from human
activity. As of 2010, urbanization has concentrated more than half of the world's population, at
least 70% of fossil fuel carbon dioxide emissions, and a significant amount of anthropogenic methane into a small fraction of the Earth’s land surface. Currently, the 10 or 20 largest cities
together represent the third largest emitter of fossil fuel CO2 after China and the US. Once urban
form and infrastructure are established, they are difficult to alter. Hence, the window of opportunity for shaping low-carbon urban futures may be closing. In order to provide a diagnosis of
urban emissions at scales relevant to urban decision-making and enable identification of lowcarbon or carbon mitigation opportunities, cities need better information about their emitting
landscape; information that not only reflects scientifically accurate methods, but places emissions
at space and time scales relevant to urban decision-making and identifies key functional characteristics (sector, sub-sector, fuel).
A number of research projects around the world have developed and tested methods for independent estimation of greenhouse gas emissions (e.g., INFLUX, Los Angeles/Paris
Megacity Project). This work has established
an urban greenhouse gas information system
that combines atmospheric monitoring, data
mining and model algorithms. IG3IS will redesign this information system to be deployable to different parts of the world, particularly in the low- and middle-income countries where GHG information needs are
Fig. 2: High spatial and temporally resolved urgreatest and capacity is limited.
ban data developed through the Hestia Project.
Our near-term objective is to build an information delivery portal for the existing global, highresolution emissions information data product. This will offer global cities with little existing
information, a starting point for CO2 emissions estimation. We follow this by more active partnerships with interested cities to build-out more resolved and process-based information systems
to actively track progress and enable efficient, optimal GHG mitigation choices based on more
detailed and accurate emissions diagnostics.
4.3 Detecting and Attributing Methane Super Emissions from the Oil and Gas Supply Chain
While atmospheric carbon dioxide is 200 times more abundant than methane, methane has 80
times more global warming potential than CO2 (molecule for molecule on a 20 year time scale).
Also unlike CO2, the amount of methane emissions from fossil fuel is not well understood, is
highly uncertain. The credibility of bottom-up inventories of CH4 emissions from the oil and gas
supply chain is difficult to construct because of the skewed distribution of emission sources and
regionally specific data. This skewed or fat-tail distribution of emission sources (super emissions
resulting from low probability, high consequence events) offers great hope for effectively locating and then controlling a significant fraction of methane emissions through a tiered suite of
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atmospheric observations: aircraft-based, ground-based in-situ or on vehicles, towers, and models. As part of this IG3IS objective, extending the significant successes demonstrated in North
America in this domain to the world’s oil and gas supply chain has excellent potential to inform
oil and gas operators and significantly
reduce methane emissions. Exploring
these solutions and applying them to
new types of sites or emissions profiles,
for example offshore platforms or coal
bed methane, can potentially provide
further reductions. IG3IS also intends
to extend these approaches to other
methane emitting sectors such as agriculture, waste and wastewater and develop sector-appropriate methodologies
in the medium term. These sectors have
close links with urban emissions as they
are much more likely to be located in or
Fig. 3: The combination of CH4 and black carbon
close to cities than oil and gas extracmeasures along with substantial CO2 emissions reduction sites.
4.4 Timely and Quantitative Support
for the Paris Agreements “Global
Stocktake”
tions [a 450 parts per million (ppm) scenario] has a
high probability of limiting global mean warming to
<2°C during the next 60 years, something that neither
set of emissions reductions achieves on its own.
A mid-term objective for the IG3IS is to provide frequent, near-realtime evaluation of the efficacy
of emissions reduction policies and measures (e.g., NDC) at national and sub-national scales. In
particular, the IG3IS approach can be used to assess the efficacy of emission reductions associated
with NDCs and emissions estimates from national inventories. A combined approach based on
the IPCC TFI protocols and the IG3IS methods will be the best means by which NDCs are evaluated under the Paris Agreement’s “Global Stocktake.” For the case of the non-CO2 GHGs, the
IG3IS approach offers the demonstrated ability for independent evaluation of emission inventories with rigorously quantified uncertainties and the potential for higher-frequency and more
timely assessments than possible with traditional inventory approaches. Such assessments could
provide critical feedback to countries on progress toward their NDCs, offering opportunities for
course-correction.
There have been many proof of concept demonstrations of how the combination of atmospheric
measurements, data mining, emissions modelling and inverse model analyses can better quantify
and track changes of NDC-relevant GHG emissions, such as the examples associated withnonCO2 GHGs [Lunt et al, 2015, and Henne et al, respectively]. For the case of fossil fuel-CO2, of
particular interest under the Paris Agreement, CO2 measurements alone contain a significant biospheric signal and are therefore necessary but not sufficient to infer fossil fuel-CO2 emissions
[Shiga et al, 2014]. However, it has been demonstrated that fossil fuel-CO2 emissions can be
inferred by inverse model analyses of a combination of atmospheric CO2, radiocarbon (14CO2)
measurements, together with measurements of other co-varying atmospheric species [Basu et al,
2016]. Combined with state-of-the-art techniques in data mining and emissions modelling, the
IG3IS approach offers the most advanced means to assess and evaluate GHG emissions. A fundamental goal of IG3IS is to disseminate these analyses and methods more broadly. The primary
limits to greater dissemination of the IG3IS approach is the number of high quality measurements
of atmospheric greenhouse gases (e.g. CO2, 14CO2, CH4, CO, HFC-134a), access to high7
resolution satellite imagery, and access to in-country socioeconomic/energy data. This translates
into an immediate priority to expand atmospheric observations in low- and middle-income nations and combine this information with new emissions modelling approaches.
5. Long-Term IG3IS Objectives
A long-term information system must have more dense and frequent observations, better transport
modeling, and improved analysis and assimilation focused on policy-relevant scales. With these
in mind, it is imperative that the system be designed and implemented in a way that supports current and emerging issues.
Earth’s carbon-climate system is undergoing profound and unprecedented change. This change is
driven globally by fossil fuel and land use change emissions that increase atmospheric concentrations of CO2 and other greenhouse gases. During the last decades, the effect of emissions on the
increase of atmospheric CO2 has been strongly attenuated by the response of the natural carbon
cycle, with ocean and land carbon sinks absorbing on average approximately half of the emissions. Future climate change is projected to weaken the capacity of natural sinks, i.e., a positive
feedback on the increase of CO2. The complex mix of accelerating and stabilizing processes in
the coupled carbon climate system may also result in sudden, non-linear tipping points, such as
shifts in natural sources/sinks magnitude (and/or polarity) or the appearance of new sources.
Changes also occur in the socio-economic processes controlling emissions – from local-scale,
such as sporadic leaks of CH4 from natural gas use, to transitions in provincial and urban economies, and in energy and food production systems. This combination of complexity across many
space-time scales and controlling processes has some parallels with well-established weather and
other environmental extremes. However, unlike weather and extreme events, society currently
has limited “situational awareness” of the coupled human-natural carbon system. Current GHG
information frameworks are limited to aggregate inventories largely based on energy statistics for
fossil fuel emissions (typically annual, national level estimates by economic sector) and researchgrade observations and models for land use emissions and natural sinks. These existing researchbased frameworks are characterized by delays and uneven global coverage. They lack sufficient
capabilities to quantify GHG fluxes and their change over time at temporal and geospatial scales
necessary to inform mitigation actions. These frameworks currently support societal assessments
at roughly 5 years cadence and national scale (with a few research-grade exceptions, e.g., the
Global Carbon Project). This is far too slow and too coarse to provide timely, relevant feedback
for decision-making on a rapidly changing planet.
While IG3IS has near-term deliverables that will guide improved knowledge on emissions and
inform new emission reduction opportunities, the long-term payoff is to enable the provision of
decision-relevant carbon situational awareness through comprehensive, reliable, sustained, frequent assessments of greenhouse gas fluxes. IG3IS can bridge the current gap between scientific
efforts and national greenhouse reporting programs. In the long-run, IG3IS will provide both diagnostics and input data for improved inventories and timely inputs for mitigation guidance,
monitoring the effectiveness of mitigation actions, and supporting long-term policy planning.
IG3IS capabilities will be similar in some respects to aspects of modern weather services – primarily the rapid delivery of current and recent carbon fluxes and controlling activity (on timescales of weeks rather than years). Potentially, IG3IS could also deliver short-term “carbon forecasts” for selected domains – if deemed valuable for decision-making (e.g., driven by recent
observations rather than long-term integrated assessment models).
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IG3IS will build upon, integrate and improve existing and planned surface-based measurement
networks, airborne and satellite observations, modeling frameworks and data assimilation systems
and where necessary, fill key gaps in those systems. As with modern weather services, the transition between research-driven and operational GHG observing and information systems for
successful long-term implementation of IG3IS presents a number of challenges. Meeting current
and future stakeholder needs will require:

frequent definition of stakeholder requirements to successfully capture the evolving
needs of GHG mitigation management,
 build partnerships with governmental and non-governmental organizations and the
private sector,
 development of a system architecture that optimizes cost and performance while
maintaining sufficient flexibility to accept new capabilities as these become available,
 a robust program plan and long-term funding strategy, and
 a roadmapping strategy that assesses gaps in both observational and informational
system needs and identifies research having potential to fill these gaps through incremental deployment and prototyping, including pilot projects, that evaluates key
component performance.
As the modern weather services enjoyed by most of the world today, WMO, its member institutions and partners have the experience and technical knowledge essential for building the IG3IS
through formulation, design, prototype, and sustaining it in its future construction, deployment
and operational phases. By leveraging existing skills from weather services and ongoing carbon
cycle research, WMO can provide the leadership and structure needed to support the stepwise
building of the IG3IS capable of meeting society’s need for decision-relevant carbon situational
awareness.
6. Next Phase of IG3IS Planning
The next step for IG3IS will be the implementation planning with the necessary details to build
systems to deliver the near- and mid-term services described above. This planning by necessity
will begin with the definition of a statement of work (SOW) and budget for these activities. Critical for the success of this step will be active entrainment of partners, users, and sponsors through
all stages of development and close coordination with UNFCCC, IPCC, GCOS, GFCS, GEO
Carbon Flagship, WCRP and their constituencies.
This activity will result in delivery of the IG3IS Program Roadmap to the sponsors and key stakeholders culminating in a formal review in summer 2017. If approved, the Program Concept Plan
will provide the foundation for design and implementation of IG3IS in subsequent years.
Period of performance: July 2016-June 2017
Milestones and Deliverables:
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Fall 2016 – sponsor/stakeholder meeting – establish IG3IS driving objectives and scope
Spring 2017 – complete IG3IS Program Roadmap (covering above tasks)
Summer 2017 – IG3IS Roadmap Review with stakeholders and sponsors
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References:
Lunt, M. F., et al, Reconciling reported and unreported HFC emissions with atmospheric observations, www.pnas.org/cgi/doi/10.1073/pnas.1420247112
Henne, S, et al, Validation of the Swiss methane emission inventory by atmospheric observations
and inverse modeling, Atmos. Chem. Phys., 16, 3683–3710, 2016 www.atmos-chemphys.net/16/3683/2016/ doi:10.5194/acp-16-3683-2016
Shiga, Y. P., A. M. Michalak, S. M. Gourdji, K. L. Mueller, and V. Yadav (2014), Detecting fossil fuel emissions patterns from subcontinental regions using North American in situ CO2
measurements, Geophys. Res. Lett., 41(12), 4381-4388.
Basu, S., J. B. Miller, and S. Lehman (2016), Separation of biospheric and fossil fuel fluxes of
CO2 by atmospheric inversion of CO2 and 14CO2 measurements: Observation System Simulations, Atmos. Chem. Phys., 16(9), 5665-5683.
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